Dental composites with excellent tooth-like appearance can be formed on command with the advance of photopolymerization technology. Yet compared with that of the traditional amalgam filling materials, the longevity and robustness of current dental composites are still not ideal. Well-preserved interfacial bonding between the composite and tooth is of vital importance to prevent the occurrences of compromised marginal adaptation, microleakage, and recurrent caries. Restricted polymerization shrinkage, as one of the major drawbacks of dental composites, results in disrupting contraction stress at the interface between the composites and tooth, and can be transferred to the tooth structure. In order for the composite/tooth interfacial bond strength to overcome the detrimental shrinkage stress, many approaches such as the development of low shrinkage monomer/composite materials, better bonding agents with improved bonding strength & sealing capability, and various curing and placement techniques aiming to relieve the shrinkage stress by flow have been proposed and investigated.
For the past several decades, there are extensive investigations from both academics and industries to design dental composite with low polymerization shrinkage and shrinkage stress. A variety of different resin and filler system have been studied, yet to date 2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane (Bis-GMA), Bis-GMA derivative such as ethoxylated Bis-GMA (or EBPADMA), and urethane dimethacrylate (such as 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane) based oligomers/monomers are still the predominantly used structural dental resin. There is still significant interest to develop dental resin and composite with reduced shrinkage stress. This is highly demanding mission as shrinkage stress generation and control is affected by multiple factors and requires intense research efforts to develop novel dental composites with significantly decreased shrinkage stress, without compromising strength, modulus, and a variety of other key properties.